7 Answers
7

All master level spells - be it Dead Thrall, Flame Thrall, a destruction spell or anything - are casted with two hands, and so 'dual-casting' does not apply. All also have a significant charge time.

This is irrelevant for conjuration master spells - as they are effectively permanent anyway (technically just a realllllllyyyy long time :P ) - but is important for the other schools. The lengthy cast time can often make them less effective than lower level spells and are generally only useful in certain scenarios due to their larger AoE or special effects. For base effects like pure damage, stun-lock, healing or illusion effects then dual-casted expert level spells are often more powerful.

So technically the word permanent is wrong? I checked on wiki, it says thrall spells have a duration of 86313600 secs, if they do have duration, then is it safe to say conjuration dual casting perk have an affect on thrall spells too?
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w1nger1Jan 17 '12 at 3:48

I said "effectively" :). But no, dual-casting doesn't have an effect because it is not dual-casted, it is a master level spell and is two-handed casted but it doesn't count as dual-casted. I only started talking about its duration because it affects whether the lack of dual-casting has a [b]practical[/b] effect on its usefulness. It doesn't :)
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AsdafghJan 19 '12 at 19:54

This answer isn't entirely correct, you can dual cast Master level spells. However I agree with Cor that because of the incredibly long use timer, even a single cast of Dead Thralls is sufficient. You still CAN dual cast for technically a longer thrall life.
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tiddyJul 17 '12 at 18:13

Because it can only be cast with 2 hands, there's no way to compare it's single-handed effectiveness. If the Dual-Casting perk were to, for example, double the duration of an atronach summon (Not sure what Conj DC does anyways, so just a rough guess,) maybe with the dual-casting perk, it would double the "permanent" (just very long) duration from 86313600 secs to 172627200 (even longer).

I don't know about every master spell not being affected by dual cast. I tried the dual casting perk for alteration and it raised the dragonhide duration from 45 sec. to 1 minute. I'm still trying to test everything else. As for the dual casting for master conjurations spells... The only one I could think it would help with is "dead thrall" to raise the level corpse it can raise.

What everyone seems to fail to take into consideration is that, although all master level spells are indeed casted with both hands in the spell animation, if you cast Thrall spells with your left OR your right hand, it costs significantly less mana than if you cast Thrall spells with BOTH hands. In other words, you CAN dual cast Master level spells, it's just that whether or not it does anything is still a mystery to me. I would imagine that, since dual casting conjuration sells increases the duration of the spell and since Thralls are permanent and the duration can't be increased, that dual casting either makes the Thralls more durable, or it was just a hiccup in the programming and they forgot to take off the 2.8 dual casting cost for Master level spells and it's just a waste of mana.

It doesnt matter how the visual animation looks if it looks the same. as said for example dragonhide duration is being increased by alternation dual casting so the same thing could be with conjuration dual casting Probably the level cap is changed when have the dual casting perk even if there is no Visual difference. And also probably the ritual stone time is lenghtened

"Thrall spells must be cast using both hands, you cannot allocate to the spell to just one hand."

This seems to confuse many people so I was compelled to clear this up. Dual casting does affect master skills.

For example, I have the dual casting alteration perk, which increases the power of dual cast alteration spells. If I use Dragonhide with one mouse button it still shows my avatar using both hands but it costs around 300 magicka (my magicka is around 500 at the moment). If I click both mouse buttons at the same time I do not have enough magicka to use the spell.

The outcome for Dragonhide is (even though the perk claims to make it stronger) that it actually increases the time instead. I also know that the dual casting master level destruction spells do much more damage for dead thralls or any of the atronachs that are permanent. I have not tested it yet and was hoping someone could tell me if it affects the strength of the body you are able to raise instead of doing what the perk claims since I know for a fact the alteration perk makes alterations to itself.